Sand that flows like water
Everything around us that has mass and takes up space is matter. Matter usually comes in three states: solid, liquid and gas. A stone is a solid, juice is a liquid and the air in a balloon is a gas. Even a volcano shows all three: the rock is solid, the hot melted rock that flows is a liquid, and gases rise from the crater. Sand is a puzzle. It pours from your hand like a liquid, yet it makes a pile like a solid. Look closely: each grain is a tiny solid. The grains slide over one another when you pour, so the heap flows. Note that the grains of sand are not the “particles” we study later, because those are far too small to see. Some scientists think ancient builders in Egypt may have wetted sand in front of heavy statues so that they slid more easily. Wet sand has less friction than dry sand, and it is a good question to test, not a fact we can prove here.
| Solid | Liquid | Gas |
|---|---|---|
| spoon | milk | steam from the kettle |
| bread | tea | air in a bag |
| Sand | Rubber band stretch when pulling the block (cm) |
|---|---|
| dry | 6 |
| wet | 4 |
Sand play (a grown-up helps). Pour dry sand from a cup onto a tray and look at the pile. Does it flow? Does it keep a shape? Look at the grains with a magnifier. Then write: “Sand is like a liquid because… Sand is like a solid because…”. Do not eat or throw the sand.